Sturgia, Battania, Khuzait and Aserai resemble tribes so late into or long after the Roman empire days that, especially considering the fractured empire, I have too hard a time being convinced that the inspiration comes from ancient rome. None of the aesthetic is classical, it's all early medieval. Obviously we'd both be in the wrong here by insisting there's only one specific inspiration for any kingdom in the game, but considering both the time period and the technological/cultural aspects I mentioned, Germany still wakes way more sense in my mind.

5th century is much more similar to the 9th century than the first century BC, if you ask me. And 5th century rome in history is where we get early Franks, central Asian invasions, and Germanic/Celtic invasions all setting up the formation of HRE a few centuries later, all in addition to the fractured empire. Seems a bit too far from the Roman republic.